Photochemical aging of Beijing urban PM2.5: Production of oxygenated volatile organic compounds

Abstract

PM2.5 has become the dominant atmospheric pollutant in many countries. Many components of PM2.5 are highly photoactive. However, the photochemical aging of PM2.5 remains poorly understood. In this study, the photoaging of real PM2.5 samples collected from 2017 to 2018 in Beijing under simulated solar radiation (λ ~ 340–850 nm) was investigated. Our study showed that large amounts of oxygenated volatile organic compounds (OVOCs), such as acetaldehyde, formic acid, acetone and acetic acid, were released during the photochemical aging of PM2.5. Furthermore, although a positive correlation between the OVOCs yield and the organic matter (OM) in PM2.5 was observed, the product distribution from the photoaging of PM2.5 was different from that in the direct photolysis of artificially synthesized SOA. Because of the release of OVOCs, the PM2.5 mass loss was evaluated to be ~1.80% per day under typical atmospheric conditions. The OVOCs released during the photoaging of PM2.5 may contribute substantially to the OVOCs sources omitted from troposphere chemistry models and may have a significant effect on the OVOCs distribution and oxidation capacity of the atmosphere.